Method of etching metals.



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To all whom it may concern:

Be it known that 1, Jesse L. Jones, a citizen of the United States, and a resident of Uakmont in the count of Allegheny and State of Pennsylvania, have invented a new and useful Improvement Methods of Etching Metals, of which the following is a specification.

My invention relates to methods of testing the physical properties of metals, and it has special reference to methods of etching iron, steel and other industrial metals for the purpose of microscopic examination.

The object of my invention is to provide a method of etching metals by means of;

which irregularities in composition and structure may be made evident in a simple and convenient manner.

The microscopic examination of metals by polishing thesurface of small samples and then etching with various reagents has been brought to a high degree of excellence, especially in the iron and steel industries. ]Less progress has been made, however, 1n the development of methods of rendering visible on a large scale the porosity, irregularity in composition, hair cracks, blisters, seams and other defects which are difficult to detect by visual inspection in rolled'or forged metals, where the mechanical working has rendered the surface of the metal apparently uniform.

l have discovered that iron, steel and other metals may be etched to a marked degree by immersing them for a short time in a molten metal of lower melting point. For

the treatment of iron and steel, I prefer to use molten zinc as the etching reagent, but other metals of relatively low melting point such as molten tin, lead and hot mercury may also be used. a

In etching metals according to my method,

I samples of the metals to be tested are susi it pended for one or more hours in a bath of molten zinc maintained at a uniform temperature. l have found it desirable to provide a mechanical arrangement that will keep the articles being etched in constant motion while inthe molten zinc. Five hours is a suitable immersion period for producin r' thorough etching. The samples are then taen from the molten zinc, the adherent dross and metallic zinc are broken off as Y much as possible by means of a hammer, and the samples are finally cleaned by iersing Specification of Letters Patent.

Patented ec, 4t, rat "to,

Application filed June 11, 1915. Serial No. 33,510.

in dilute sulfuric acid, which does not attack the metal of the samples-as long as any zinc remains. Metals treated in the foregoing manner are found to be etched in such a manner as to indicate very plainly the homogeneity and surface condition of the metal.

The action ofmolten Zinc upon steel and till areas, which in comparison are scarcely attacked at all.

Another application of the foregoing methodis in the examination of high-speed steels containing additions of tungsten, chromium, manganese, vanadium, cobalt, etc; These steels are etched in a very irregular manner which indicates that the constituent metals are seldom, if ever, perfectly alloyed. The deeply etched spots in such steels are probably very high carbon areas that are vigorously attached by the molten ainc.

While it have specifically described the treatment of iron and steel samples with molten zinc, it is to be understood that my invention is not restricted to the examination of iron and steel or tothe use of zinc as the etching reagent. The use of molten lead for etching platinum and platinum-,

iridium alloys has-been found advantageous. Any metal or mixture of metals may be used as the etching reagent which is molten at a lower temperature than the metal to be etched, and it is therefore tobe understood that my invention comprises all modifica tions in materials and methods that fall within the scope of the appended claims.

ll claim as my invention:

1. The method of etching metals that comprises immersing the metal to be etched in a molten metal of lower melting point that is capable of alloying with the metal to be etched, removing the etched metal from the molten bath, breaking ofi the adherent ma- AME Wit

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terial, and treating theetched metal with a solvent of the reagent metal.

2. The method of etching metals capable of alloying with zinc that comprises immersing the metal to be etched in molten zinc, removing the etched metal from the molten bath, breaking ofl' the adherent material, and treating the etched metal with dilute sulfuric acid.

3. The method of etching metals that comprises immersing the metal to be etched in a molten metal of lower melting point that is capable of alloying with the metal to be etched agitating the said molten metal, removing the etched metal from the molten bath, and cleansing the said etched metal.

In testimony whereof, I have hereunto subscribed my name this 27th day of May,

JESSE L. JONES. 

